[Electron microscopy research on the chromatin structure of dispersed lampbrush chromosomes in the hen]

Abstract

The lampbrush chromosomes from the late previtellogenic and early vitellogenic oocytes of adult hens were spread according to Miller's technique and examined in electron microscope. The nucleosomes in the threads of the non-transcribed chromatin are uniformly distributed, the spaces between the nucleosomes correspond by their length to the linker DNA. Nucleosomes are absent in the transcriptional units with high intensity transcription. In transcriptional units with moderate and weak transcription the nucleosomes are identified in the axial chromatin fibril between RNA-polymerase granules, the space between them varying. The compactization ratio of DNA (the number of DNA mkm in a 1 mkm chromatin fiber) in non-transcribed fibrils is equal to 2.1, in transcriptional units with moderate and weak activity it is 1.7, and in transcriptional units with intensive transcription it is close to 1. The DNA compaction ratio in lateral loops of lampbrushes is determined by the intensity of transcription. It is supposed that in the native state the inactive chromatin with uniform spacing of nucleosomes has a supernucleosomal structure, while the DNA compaction ratio in the transcribed sequences corresponds to that on Miller's spreads.